Process for producing steel



UNITED STATES ALBERT PATENT OFFICE.

voeLnn, or non'rmunn, GERMANY, AssiGNoR. BY MESNE ASSIGNMENTS, TO

THE CHEMICAL FOUNDATION, INC., A CORPORATION OF DELAWARE Pao'cEss FORPRODUCING STEEL.

No Drawing.

ess and has for its object so to conduct the de-phosphorization of themetal as to cause the whole of the phosphorus to be converted intoliquid citrate-soluble slag.

The attainment of this double object,

namely, the conversion of the slag into the liquid state and of thewholephosphorus into a citrate-soluble phosphate has hitherto met withdifliculties due more particularly to the antagonistic tendencies of theconditions under which these two steps of the process must occur.

It is to be noted that the slag only becomes fiuid enough to permit itsremoval at the high temperature at whichthe so-called re-phosphorizationbegins, that is to say, at

which a portion of the phosphorus already absorbed by the slag isreduced by the car-- bon of the bath and is brought back again into themetal. As a result of this the steel could not be brought down to thelow con- I tent of phosphorus required for high grade carbon steel. V

The object of this invention is attained by dividing the process ofde-phosphorization into two temperature Zones, the final stages of thede-phosphorization being determined by an intensive beginning-of thede-carburization.v This period is recognized by the abundant occurrenceon the bath of the small blue flames of carbon monoxid.

This invention further relates to'a mode of producing steel in anopen-hearth furnace from iron rich in siliconaccording to the pig ironand'ore process. Inthe use of iron very rich in silicon the silicic acidwhich is formed renders the slag so thin as to cause the content ofphosphoric acid to fall below the economically admissible limit. By thepresent process there is obtained a slag rich in hosphate from a pigiron rich in silicon. he process is carried out in such a manner, thatin the basic furnace there 1s formed and removed an acid slagSpecification of Letters Batent. I Patented June 8, 1920. Applicationflied January 24, 19.14, Serial 1%. 814,194. i

which absorbs the greatest part of the silicon and contains onlytraces'of phosphoric acid, while in the bath there remainphosphate-forming constituents, from which is ormed by addition of basicmaterial a slag. rich in citrate-soluble phosphates.

By this method it is possible so to conduct the process that the silicicacid and the phosphoric acid are slagged separately. To the SlllCOIliron charged into the hearth furnace as much ore is added as isnecessary for oxidizing the silicon. The addition of lime,however, isdispensed with or at least is reduced to a minimum. Almost imme-.

diately after the ore charge has been made, an acid slag is formed whichowing to its acid character contains only traces of phosphoric acid.-The slag is blown'oflt or tapped off as soon as the metal bath ispurified of slag, after which steps are taken for recuperating thephosphate slag.

Example.

To a pig iron charge containing about 3.5% of carbon, 1.5% or more ofsilicon, 0.6% of phosphorus or more ore is added for the oxidation ofthesilicon. There immediately ensues a violent reaction which yields a slagof about 32% SiO The slag is-removed and ore and lime are added afreshand the charge is now treated with a View to recuperating the powderedThomas phosphate slag. This phosphate slag still contains,-even at theabove-mentioned low contents of phosphorus more than 14% ofcitrate-soluble phosphoric acid so that it is still useful for.commercial purposes. The

phosphate slag is preferably removed before intensive decarbonizationbegins to avoid rephosphorization, and the refining of the charge isthen finished.

What I claim is 4 1. The process of producing steel in a basicopen-hearth furnace from iron rich in silicon by the pi iron and oreprocess, which consists in rst forming an acid slag containingpractically all the silicon and only traces of phosphoric acid, drawingoff this acid slag, and then forming within the same furnace and withthe metal remaining therein a basic slag rich in citrate-solublephosphates, drawing oil this slag and finally refining the steel.

2. The process of converting the phosphorus content of molten iron intoliquid citrate-soluble phosphate slag, which consists in first removingthe silicon as an acid slag While in a basic furnace, maintaining thetemperature of the charge below the point of intensive decarbonizationwhile slagging phosphorus in the same furnace, removing the phosphateslag, and finally -refining the metal. H

3. The process of producing steel in' a basic open-hearth furnace fromiron rich in silicon by the pig-iron and ore process,

which consists in first forming by addition of iron ore an acidslagcontaining practically all the silicon phoric acid, drawing off andonly traceslof hosthis acid slag, and

then forming by addition of iron ore. and

lime Within the same metal bath rezr laining l'lCh in citrate-solublefurnace and with the therein abasic slag phosphates, drawing ALBERT VWitnesses:

' HELEN NUFER,

GGLER. [L. 5.]

ALBERT N UTER.

